The present invention is related to an expansible type triangular umbrella ribs and the related collapsing mechanism, by means of an expansible first main rib to penetrate through the pivotal connection of a second main rib and a linking rib to freely slide therealong, and to let the first main rib, the linking rib and a first support rib form a triangular linking-up umbrella rib structure; by means of the protruding circular tail arranged at the top end of the second step of the central shaft to stabilize the lower nest and to prevent the lower nest from breaking away when the umbrella is opened.
Regular foldable umbrella rib structure is as shown in FIG. 1, wherein the ribs (1') (2') (3') (4') are pivotally connected one another to form a configuration similar to parallelogram ABCD. When the umbrella is opened, AD, BC, CD are not in a straight line, and a space D is left between AD and BC. When an outer force is applied upon the umbrella rib structure, a torsional force will rise through space D, to interfere with or damage all pivotal connecting points to further loosen the rib structure and shorten the service life of the umbrella.
The central shaft of regular multi-fold type umbrella (as shown in FIG. 8) is a multi-stepped type. The upper step has bigger caliber and the lower step has smaller caliber. The more the number of the steps is provided, the bigger the difference of the caliber will be. When the umbrella is opened, the lower nest plate (20') is moved to the top dead point to let the stopper (311') be retained in the locating hole (201') of the lower nest plate (20'). In this arrangement, the inner diameter of the lower nest plate (20') is bigger than the central shaft (34'), and there is a distance P left between the lower nest plate (20') and the central shaft (31') when the lower nest plate (20') is moved to the top dead point. Therefore, the lower nest plate (20') tends to vibrate. If the lower nest plate (20') is inclined to the lateral side where the stopper located, the distance P will be doubled, and the lower nest plate (20') may break away from the constraint of the stopper to let the umbrella be collapsed.
In view of said problems, the present invention is thus created to be intended for elimination of the above-described drawbacks.